The present disclosure relates generally to drilling fluid monitoring in subterranean drilling applications. More particularly, this disclosure relates to a method and system for monitoring the weight, mass, or density of drilling fluid.
During the drilling of a subterranean well in the quest for hydrocarbons, drilling fluid, also referred to in the art as “drilling mud,” is circulated downwardly through a drill pipe and through a drill bit attached to the drill pipe. After exiting the drill bit, the drilling fluid flows into an annulus formed by the drill pipe and a bore wall of the well and return upwardly through the annulus to the surface. When the drilling fluid reaches the surface, the drilling fluid is directed to a shaker which separates cuttings from the drilling fluid. After passing through the shaker, the drilling fluid flows to a settling tank which is designed to further remove cutting particulates from the drilling fluid. The drilling fluid then travels to a suction tank where mud pumps return the drilling fluid back to the drill pipe and the well.
The drilling fluid is essential to a well drilling operation as the drilling fluid serves to carry the cuttings away from the drill bit area and out of the well. The drilling fluid also acts as a stopper in the well to prevent blowouts by exerting hydrostatic pressure on the bottom of the well to balance or overcome the pressure of any upwardly acting hydrostatic pressure disposed inside the formation adjacent to the well, such as the pressure of gas, water, or oil which may be exposed in drilling. While the hydrostatic pressure of the drilling fluid must be great enough to balance or overcome the formation pressure in the well, the hydrostatic pressure of the drilling fluid must also not be so great as to cause circulation losses of the drilling fluid in the well. Circulation losses occur when the hydrostatic pressure of the drilling fluid exceeds the formation pressure inside the well thereby causing the drilling fluid to escape out of the well and into the formation.
The drilling fluid generally includes caking agents that allow the drilling fluid to also seal the bore wall of the well. As the drilling fluid circulates through the well, the caking agents accumulate onto the surface of the bore wall of the well to seal the well and help prevent the drilling fluid from flowing out of the well and into the porous material of the formation.
As conditions vary in the course of drilling, the weight of the drilling fluid can also be affected by the changing conditions. For instance, if the drill bit penetrates a formation containing gas, the gas can enter the well and mix with the drilling fluid thereby reducing the density of the drilling fluid. Reducing the density of the drilling fluid can cause the drilling fluid to flow out of the well at a faster rate than the drilling fluid is entering the well, resulting in a loss of hydrostatic pressure of the drilling fluid in the well. Such a condition must be detected immediately as remedial action may be necessary to increase the density of the drilling fluid entering the well to restore balance between the hydrostatic pressure of the drilling fluid in the well and the formation pressure adjacent the well. If remedial action is not taken, the lack of balance between the hydrostatic pressure of the drilling fluid in the well and the formation pressure adjacent the well can result in a blowout of the well.